Starting with the last paragraph where we have finished with DNA structure Now it’s obvious that DNA looks a very attractive molecule for life processes. Thanks to Henri Becquerel discoverer of radioactivity, Its gives a perfect way to Alfred Day Hershey and Martha Cowles Chase to prove DNA on protein as a genetic material. DNA Which have ability to move forward for Transcription process which finally lead to synthesis of new polypeptide chain (a unit of protein) with process known as translation.
Proteins are considered as body building material, and as all enzymes are protein, it makes proteins very essential for metabolic activities. So discovery of DNA as a genetic material reveals the secrets of life i.e. how conservation of species and their phenotypic character is possible.
Factors required for transcription
A. Prokaryotic
1. RNA polymerase (enzyme that catalyzes the synthesis of RNA from a DNA template).
a) Core enzyme = 3 different types of subunits (2a; 1b; 1b’)
(1) b - binds incoming nucleotides
(2) b’ – binds DNA
(3) a - helps with enzyme assembly; interacts with other transcriptional activator proteins; recent work demonstrated that a also interacts with some DNA sequences
b) Holoenzyme = core + s factor (recognizes the promoter)
c) s factors – Initially, people thought that there was only one s factor that functioned to direct RNAP to the promoters of genes. Later, different classes of s factors were found. Each s factor directs RNAP to a different type of promoter (differentiated by a specific DNA sequence in the promoter).
2. Accessory transcription activator proteins
a) IT have ability to bind with specific DNA sequences and help RNA polymerase to initiate transcription via protein-protein interactions or by altering the structure of the DNA.
b) Transcription of some promoters requires an accessory transcriptional activator; at other promoters, the activators just increase the rate of transcription but are not absolutely required.
3. Template DNA containing gene or genes to be transcribed
4. Promoter - The regulatory element that determine when a gene “turned on” (transcribed) or “turned off”. The promoter DNA is located upstream of the gene and contains a sequence which is factor of RNAP and other transcription factors bind. Different classes of promoters have different DNA sequences. Deviations from the consensus sequence decrease the level of transcription.
5. Weak promoters (ones that have poor sigma recognition sequences) have additional sequences to which transcriptional activators can bind.
6. NTPs, Mg2
Gourav KumarFaculty cum Research associate
Bioinformatics Institute of India
